Optoelectronic circuit board with optical waveguide and optical backplane

ABSTRACT

An optical transmission device comprises an optical transmission medium and a plurality of optical receivers, and the optical transmission medium has a linear line waveguide. At least one of the optical receivers is adapted to receive a first optical signal propagated through the line waveguide, while at least one of the optical receivers is adapted to receive a second optical signal propagated through the optical transmission medium.

TECHNICAL FIELD

The present invention relates to an optical transmission deviceincluding a two-dimensional (2D) or three-dimensional (3D) opticaltransmission medium and a line waveguide and also to an optoelectroniccircuit including such an optical transmission device and therebycomprising a mixture of electronic circuits and optical circuits.

BACKGROUND ART

In recent years, information processing instruments such as personalcomputers, mobile phones and PDAs (personal digital assistants) havebeen required to show a high processing speed in addition to be compactand lightweight. However, as the processing speed rises, there arisevarious problems including wire-attributable delays and EMIs(electromagnetic interferences).

Proposed techniques for avoiding wire-attributable delays and EMIsinclude the use of an optical wire or a line waveguide (U.S. Pat. No.5,357,122).

Optical wires provide advantages including high speed transmissioncapabilities and being intrinsically free from electromagneticinductions. However, in the above-mentioned technique using a linewaveguide, optical wires having a thickness between several microns andtens of several microns are used and the wiring pattern is fixed.Therefore, the use of such a line waveguide is accompanied by a numberof problems including the need of using a large number of opticalswitches, the difficulty of aligning optical axes, the need ofmicro-processing the optical waveguide, the use of a large number ofparts and the difficulty of preparation if an enhanced degree of freedomfor wiring and alteration of an optical circuit is to be desired.

U.S. Pat. No. 5,191,219, on the other hand, discloses an informationprocessing apparatus comprising means for forming a planar opticalwaveguide which extends in two dimensions and serves as a shared medium,a plurality of light-emitting means and a plurality of light-detectingmeans extending in a two-dimensional arrangement over the planar opticalwaveguide for broadcasting light signals and abstracting light signals,respectively, into and from the planar optical waveguide, and aplurality of subsystems including input and output ports for processingthe light signals in the shared medium, the light-detecting means beingcoupled to input ports and the light-emitting means being coupled tooutput ports of the subsystems.

However, the information processing apparatus disclosed in the aboveU.S. patent document is not satisfactory in terms of the degree offreedom for optical wiring.

DISCLOSURE OF THE INVENTION

An optical transmission device according to the invention comprises anoptical transmission medium and a plurality of optical receivers, andthe optical transmission medium has a linear line waveguide. At leastone of the optical receivers is adapted to receive a first opticalsignal propagated through the line waveguide, while at least one of theoptical receivers is adapted to receive a second optical signalpropagated through the optical transmission medium. The opticaltransmission medium is typically a sheet-shaped two-dimensional opticalwaveguide. However, it may alternatively be a three-dimensional opticaltransmission medium, which may be cubic or spherical. Since atwo-dimensional or three-dimensional optical transmission medium and alinear line waveguide are arranged in a mixed state in the abovearrangement, it is possible to realize an optical transmission devicethat is adapted for high speed/operation with flexibility and isstructurally compact.

There can be a number of different modes of carrying out the inventionthat can be provided with the above-described basic arrangement.

Part of the second optical signal may be so arranged as to pass at leastpart of the line waveguide. It may also be so arranged that an opticaltransmission device according to the invention comprises a plurality ofoptical transmitters and the first optical signal transmitted from atleast one of the optical transmitters is propagated through the linewaveguide while the second optical signal transmitted from at least oneof the optical transmitters is coupled to a non-line section of theoptical transmission medium, which is the part thereof other than theline waveguide, and propagated through the optical transmission medium.Additionally, it may be so arranged that the transmission route of thefirst optical signal and that of the second optical signal intersecteach other as viewed from the top surface of the optical transmissionmedium.

It may be so arranged that the line waveguide is made to show a complexrefractive index greater than that of the non-line section of theoptical transmission medium, which is the part thereof other than theline waveguide, so that light being propagated in parallel with the partis guided and propagated with priority. The difference of the complexrefractive indexes is preferably not greater than 1%, more preferablynot greater than 0.5%, when light being propagated through the entireoptical transmission medium passes through the line waveguide, so as toreduce the influence thereof (in other words, so as to reduce the lossand the refraction when light being propagated through the non-linesection strikes the line waveguide and is transmitted through it).

The ½-th power of the cross sectional area of the line waveguide ispreferably not greater than ¼, more preferably not greater than ⅛, ofthe thickness of the sheet-shaped optical transmission medium so as tobe able to prevent light being propagated through the opticaltransmission medium from being coupled to the line waveguide.

It may be so arranged that an optical signal in a single mode ispropagated through the line waveguide while an optical signal in amulti-mode is propagated through the optical transmission medium. It maybe so arranged that the optical signal being propagated through theoptical transmission medium in a multi-mode has a beam-shaped profile orit is propagated only through a particular region or it is propagatedthrough the entire optical transmission medium.

The optical transmitters may be embedded in the optical transmissionmedium. The optical transmitters may have a plurality of light emittingelements and light from at least one of the light emitting elements iscoupled to the line waveguide and light from at least one of the lightemitting elements is coupled to the non-line section.

An optoelectronic circuit according to the invention comprises anoptical transmission device as defined above and an electric wiringlayer including electric wires and electronic devices, the opticaltransmission device and the electric wiring layer being laid one on theother, and the electric devices are connected to the opticaltransmitters or the optical receivers by way of the electric wires.

Such an optoelectronic circuit according to the invention may comprisean optical transmission device according to the invention and anelectric wiring layer that are laid one on the other so that it is freefrom problems including signal delays of electric wiring and EMIs andadapted to raise the degree of design freedom as circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are schematic illustrations of an embodiment ofoptical transmission device according to the invention;

FIG. 2 is a schematic cross sectional view of an exemplar line waveguidethat can be used in the optical transmission medium;

FIGS. 3A, 3B and 3C are schematic cross sectional views of an opticaltransmitter and its vicinity of an embodiment of optical transmissiondevice according to the invention;

FIGS. 4A and 4B are schematic plan views of the optical transmissiondevice used in Example 2;

FIG. 5 is a schematic plan view of the optical transmission device usedin Example 3;

FIG. 6 is a schematic cross sectional view of the optoelectronic circuitformed by laying an electronic circuit and an optical circuit and usedin Example 4;

FIGS. 7A and 7B are schematic exemplar illustrations of propagation ofoptical signal in an optical transmission medium; and

FIG. 8 is a schematic plan view of the ports of an optical transmissiondevice according to the invention, showing an exemplar arrangementthereof.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, an embodiment of optical transmission device according to theinvention will be described by referring to FIGS. 1A through 1C.

In FIGS. 1A through 1C, there are shown a film-shaped two-dimensionaloptical transmission medium 101, optical signals 103A and 103B, a linewaveguide 108, optical transmitters (optical transmitter sections) 121Aand 121B and optical receivers (optical receiver sections) 122A and122B. The optical receivers 122A and 122B receive an optical signalpropagated through the optical transmission medium 101 or the linewaveguide 108 and convert the received optical signal into an electricsignal.

The film-shaped optical transmission medium 101 has the line waveguide108 in the inside thereof. When, for example, a linear part showing arefractive index of n2 is arranged in the inside of an opticaltransmission medium showing a refractive index of n1 (n2>n1), it ispossible to propagate light with priority as the light is guided by thatpart. Such a linear structure is referred to as a line waveguide in thisletter of specification regardless of its structure so long as itprovides an optical path that guides light and propagates it withpriority. All the part of the optical transmission medium other than theline waveguide is referred to as non-line section. Thus, for the purposeof the present invention, a two-dimensional or three-dimensional opticaltransmission medium is an aggregate of a line waveguide and a non-linesection.

For the purpose of the-present invention, at least one of the opticalreceivers is adapted to selectively receive a first optical signalpropagated through the line waveguide. Additionally, at least one of theoptical receivers is adapted to receive a second optical signal freelypropagated through the optical transmission medium (the line waveguideand the non-line section). In the case of the embodiment of FIGS. 1Athrough 1C, the optical receiver 122A is adapted to selectively receivea first optical signal 103A propagated through the line waveguide 108and the optical receiver 122B is adapted to receive a second opticalsignal 103B freely propagated through the optical transmission medium101. However, the present invention is by no means limited thereto andalternatively each of the optical receivers may be adapted toselectively receive an optical signal from the line waveguide or anoptical signal from the non-line section. Still alternatively, each ofthe optical receivers may be so adapted as to receive both an opticalsignal from the line waveguide and an optical signal from the non-linesection.

While signal transmission using the line waveguide 108 takes place onlyon a fixed wiring basis, free signal propagation can occur when theoptical transmission medium 101 is regarded as two-dimensional opticalwaveguide (free two-dimensional space). More specifically, as shown inFIGS. 7A and 7B, the optical signal 103B is beamed to be propagated in aparticular region or broadcasted for the entire two-dimensional opticalwaveguide in a diffused manner. Still additionally, a particular routingcan be arbitrarily defined for the purpose of propagating it. Due to theuse of a two-dimensional optical waveguide, it is possible to arrangeoptical devices at desired positions and optical data can betwo-dimensionally transmitted from a port arranged at a desired positionto another port also arranged at another desired position.

Thus, according to the invention, information can be freely transmittedin any desired direction by using an optical transmission medium astwo-dimensional or three-dimensional optical waveguide while a linewaveguide is used for fixed optical wiring. Differently stated, a linearoptical waveguide and a two-dimensional or three-dimensional opticalwaveguide (optical transmission medium) that can two-dimensionally orthree-dimensionally freely propagate light can be made to share the samespace and can be selectively used.

An optical transmission device according to the invention may comprise aplurality of optical transmitters. At least one of the opticaltransmitters may be adapted to propagate an optical signal through theline waveguide, while at least one of the remaining optical transmittersmay be adapted to couple an optical signal to the non-line section andfreely propagate it through the optical transmission medium. In the caseof the embodiment of FIGS. 1A through 1C, the optical transmitter 121Atransmits a first optical signal 103A that propagates through the linewaveguide 108, whereas the optical transmitter 121B transmits a secondoptical signal 103B that freely propagates through the opticaltransmission medium 101.

Furthermore, a plurality of optical ports that operate both as opticaltransmitters and as optical receivers may be connected to the opticaltransmission medium. With this arrangement, the plurality of opticalports can share the optical transmission medium for opticalcommunications. Additionally, the degree of freedom of connectingoptical circuits is improved when the line waveguide and thetwo-dimensional or three-dimensional waveguide are freely used. Both ofthem can be used simultaneously or selectively by switching the mode ofpropagation.

It may be so arranged that light that propagates freely, using theoptical transmission medium as two-dimensional or three-dimensionaloptical waveguide, partly passes through the line waveguide. Then, theline waveguide and the two-dimensional or three-dimensional opticalwaveguide literally share the same space. Particularly, the differencebetween the refractive index of the optical transmission medium and thatof the line waveguide is made small so that light can pass through theline waveguide (and light may not be lost or scattered to a large extentwhen passing through the line waveguide). The difference is preferablynot more than 1%, more preferably not more than 0.5%, although it mayvary depending on the system comprising the optical transmission mediumand the line waveguide. A distribution refractive index type linewaveguide may be used.

While the above-described arrangement is advantageous from the viewpointof easiness of preparation, signal interferences may be apprehended.However, signal interferences that can occur when light that is freelypropagating the optical transmission medium is coupled to the linewaveguide can be practically eliminated in a manner as described below.For example, the problem can be eliminated when the diameter of the linewaveguide is made sufficiently smaller than the thickness of thesheet-shaped optical transmission medium. Preferably, the ½-th power ofthe cross sectional area of the line waveguide (core section) is notgreater than ¼, more preferably not greater than ⅛, of the thickness ofthe sheet-shaped optical transmission medium, although the value mayvary depending on the selected threshold for signal error rate. Forexample, the use of a line waveguide having a diameter of 10 microns maybe satisfactory when the optical transmission medium has a thickness of100 microns. Additionally, the above cited problems can be furtherreduced when the route of propagation of light is (the positions of thetransmitters and the receivers are) so designed in advance that passinglight strikes the line waveguide with a sufficient angle, for instancean angle close to right angles, relative to the latter.

On the other hand, it is preferable that the line waveguide shows arefractive index that is greater than those of the componentssurrounding it for the purpose of preventing light that is propagatingthrough the line waveguide from leaking into the two-dimensional orthree-dimensional optical waveguide. In other words, the line waveguideis preferably provided with a core-clad arrangement commonly used.

The line waveguide and the two-dimensional or three-dimensionalwaveguide can be used simultaneously when the problem of interferencesdoes not arise between them. Additionally, it is possible to make theroute of propagation of light in the line waveguide and the one in thetwo-dimensional or three-dimensional waveguide intersect each other toremarkably raise the degree of freedom of optical connections.

Signal interferences can be avoided almost completely when an opticaltransmission device according to the invention is designed in a manneras described above. However, if interferences occur inevitably due tothe design of the device, they can be avoided by means of time divisionmultiplexing or wavelength division multiplexing. Such an arrangementstill provides the advantage of sharing the same space and that ofselecting free propagation or fixed propagation.

Now, the structural relationship between the line waveguide and thetwo-dimensional or three-dimensional waveguide will be described byreferring to FIG. 2. FIG. 2 is a schematic cross sectional view ofexemplar line waveguides 108 that can be used in the opticaltransmission medium 101 of an optical transmission device according tothe invention. The cross sectional views of the line waveguides 108 inFIG. 2 include rectangular, circular and elliptic.

All the line waveguides may be buried in the optical transmission mediumor only part of them may be buried. In the case of a line waveguidehaving a rectangular cross section, one of the sides thereof may be madeto be flush with the surface of the optical transmission medium. In FIG.2, 108(a) is a line waveguide 108 having a square cross section andburied in the middle of the optical transmission medium 101 and 108(b)is a line waveguide having a rectangular cross section and buried in theoptical transmission medium 101 in such a way that one of its side ismade to be flush with the top surface of the optical transmission medium101, whereas 108(c) is a line waveguide having a circular cross sectionand buried in an upper position of the optical transmission medium 101and 108(d) is a line waveguide having a trapezoidal cross section andarranged on the optical transmission medium 101. In FIG. 2, 108(e) is aline waveguide having a semicircular cross section and arranged at thetop surface of the optical transmission medium 101 and 108(f) is a linewaveguide having a circular cross section (which may be an opticalfiber) and provided with a core 132 and a clad 131, the line waveguide108(f) being buried in the optical transmission medium 101.

As described above, the complex refractive index of the line waveguidepreferably shows a value close to that of the complex refractive indexof the non-line section. For example, the difference is to be madesmaller than several percents. This arrangement can significantly reducethe loss of light when light being propagated through thetwo-dimensional or three-dimensional optical waveguide is made to passthrough the line waveguide. A small difference of the complex refractiveindexes is preferable additionally because it can reduce the number ofpropagation modes to realize a high speed transmission in the linewaveguide when the non-line section operates as clad for the linewaveguide.

As pointed out above, it is possible to provide a wide margin forinterferences by reducing the diameter of the line waveguide relative tothe thickness of the two-dimensional or three-dimensional waveguide.Additionally, it is possible to allow only an optical signal in a singlemode to be propagated through the line waveguide when its diameter ismade sufficiently small. More specifically, in a preferable embodimentas shown in FIG. 2, the non-line section is used as clad for the linewaveguide 108 and the difference between the refractive index of theline waveguide and that of the non-line section is made small while thediameter of the line waveguide 108 is reduced. A typical example of thistechnique may be to allow only an optical signal in a single mode to bepropagated through the line waveguide. On the other hand, a multi-modepropagation takes place in the two-dimensional or three-dimensionaloptical waveguide because of the large thickness thereof. This ispreferable from the viewpoint of easiness of designing it and opticallyaligning it with optical devices.

Meanwhile, in the case of transmission of information using atwo-dimensional or three-dimensional optical waveguide, where light ispropagated with a radiation angle Øa, the intensity of light at thesignal receiving site is reduced proportionally relative to L/(RØa) (L:size of optical receiver, R: distance). Additionally, propagation oflight with a large radiation angle entails waste of light except in thedirection in which light is received. Since an optical circuit providedwith the advantages of a line waveguide and those of a two-dimensionalor three-dimensional waveguide is realized in a single opticaltransmission device (optical transmission layer) according to theinvention, the above problem can be reduced by selectively using thewaveguides depending on the situation of the device. Typically, in apreferred mode of carrying out the invention, the line waveguide will beused for high speed signal transmissions whereas the opticaltransmission medium, or the two-dimensional or three-dimensionalwaveguide, will be used for free but relatively low speed transmissions.Since a line waveguide allows communications with a sufficiently highintensity of light, it can transmit data reliably at high speed.

The reliability of high-speed data transmission will be improved furtherif the line waveguide is designed so as to allow only one or more thanone propagation modes (e.g., a single mode waveguide that allowstransmission of light only in a fundamental mode).

The line waveguide may be used exclusively for 1:1 fixed wiring, whereasthe two-dimensional or three-dimensional optical waveguide may be usedfor free connections that may include 1:n broadcast communications andm:n communications. In other words, while a large number of opticalswitches are required for free connections using a conventional linewaveguide, according to the invention, free connections can be realizedwith ease by using a two-dimensional or three-dimensional opticalwaveguide, while high speed communications will be allowed to take placeby arranging a line waveguide in advance on a critical paths that may berequired for high speed communications. Thus, 1:1 high speedcommunications and low speed communications such as 1:n communicationsand m:n communications can take place in a single layer simultaneously.

Furthermore, since a line waveguide is buried in a two-dimensional orthree-dimensional waveguide, it is possible to realize a compactcommunications system that does not have a large number of layers at lowcost. Additionally, since a line waveguide is arranged on a criticalline according to the invention, the labor for aligning the waveguideand optical device is lightened because it is no longer necessary torigorously align all the related elements. Still additionally, sinceboth the two-dimensional or three-dimensional waveguide and the linewaveguide are arranged in a single layer to reduce the total number oflayers, it is possible to produce a low profile and high density circuitboard at low cost.

Now, the components of an embodiment of optical transmission device willbe described below.

An appropriate material selected from glass, a semiconductor, an organicmaterial or the like can be used for the optical transmission medium 101so long as the selected material shows a transmittance that issufficiently high relative to light to be propagated. For example, aglass substrate, a single crystal substrate of lithium niobate or thelike, a semiconductor substrate of Si, GaAs or the like or an organicsheet of polycarbonate, acryl, polyimide, polyethylene terephthalate orthe like that is commercially available may be used without processingit specially. Additionally, vacuum evaporation, dipping, application orsome other film forming technique may be used for preparing the opticaltransmission medium 101. Similarly, the optical transmission medium 101may be prepared by injection molding, extrusion molding or some othermolding technique. A clad layer may be formed by using a coating processof forming a layer having a different refractive index. As for the sizeof the optical transmission medium 101, it may be typically between 100microns and tens of several centimeters in view of the fact thatinformation is transmitted between two-dimensionally orthree-dimensionally arranged positions, although the informationtransmission speed may have to be taken into consideration. The opticaltransmission medium 101 can have a thickness between 10 microns andseveral centimeters, although the thickness is preferably between 50microns and several millimeters from the viewpoint of ease of opticalalignment.

Materials listed above for the optical transmission medium 101 can alsobe used for the line waveguide 108 that is part of the opticaltransmission medium 101. As pointed out above, the line waveguide has across sectional area that is sufficiently smaller than the thickness ofthe optical transmission medium and may be within a range between amicron and hundreds of several microns. While the line waveguide isnormally linear, it may alternatively be curved and/or branched.

Light emitting elements that can be used for the optical transmittersinclude laser diodes and LEDs. A plurality of light emitting elementsmay be arranged for a single optical transmitter. For example, a lightemitting element that is coupled to the line waveguide and a lightemitting element that is coupled to the non-line section may beprovided. Alternatively, a plurality of light emitting elements may becoupled to the non-line section and so arranged as to show differentdirections of propagation of light.

An optical coupler to be used for an optical transmitter is preferablyadapted to radiate light from a light emitting element toward thetwo-dimensional or three-dimensional waveguide with a predeterminedradiation angle. From this viewpoint, a lens, a prism, a mirror or agrating may be used for it. Particularly, the use of a conical,pyramidal or spherical mirror is preferable because it can radiate lighttoward the two-dimensional or three-dimensional waveguide with apredetermined radiation angle.

FIGS. 3A, 3B and 3C are schematic cross sectional views of an opticaltransmitter 121 and its vicinity of an embodiment of opticaltransmission device according to the invention. FIG. 3A shows a lightscattering body 141 adapted to operate both for optical coupling to theline waveguide 108 and optical coupling to the two-dimensional orthree-dimensional waveguide 101. More specifically, light emitted fromthe optical transmitter 121 may be irradiated onto part of the lightscattering body 141 locally so as to be coupled to the line waveguide108. Alternatively, it may be irradiated onto the entire lightscattering body 141 so as to be diffused and propagated broadly in alldirections. Switching from local irradiation to overall irradiation andvice versa can be controlled by means of a mirror (not shown) orproviding in advance a light emitting element for local irradiation anda light emitting element for overall irradiation and selectively drivingeither one of them. The use of two light emitting elements may bepreferable because it is possible to independently and simultaneouslyoutput an optical signal 103A to the line waveguide 108 and anotheroptical signal 103B to the two-dimensional or three-dimensionalwaveguide 101.

FIG. 3B shows a mirror 142 and a light scattering body 141 adapted tooperate respectively for optical coupling to the line waveguide 108 andfor optical coupling to the two-dimensional or three-dimensionalwaveguide 101. In this instance again, two light emitting elements maybe provided and selectively used. Optical coupling to the line waveguide108 can be made more reliably when the line waveguide 108 is arranged ata position close to the optical transmitter 121 (on the lighttransmission medium 101 in FIG. 3B).

In FIG. 3C, the optical transmitter 121 is buried in the lighttransmission medium (coat layer) 143. Light emitted from the opticaltransmitter 121 vertically downward (downward in FIG. 3C) is scatteredby the light scattering body 141 and coupled to the two-dimensional orthree-dimensional waveguide 101. On the other hand, light emitted fromthe optical transmitter 121 horizontally (transversally in the figure)is directly coupled to the line waveguide 108. This arrangement ispreferable for realizing a compact device.

Meanwhile, optical receivers may be arranged to correspond to theoptical transmitters 121 of FIGS. 3A through 3C (to invert the arrowsrepresenting optical signals). Preferably, they are arranged so as toreceive light from all directions of the two-dimensional orthree-dimensional waveguide 101. With such an arrangement, all theoptical receivers may be made to have the same and simple configuration.Of course, optical receivers may be so arranged as to receive light frompredetermined directions of the two-dimensional or three-dimensionalwaveguide 101.

Light receiving elements that can be used for the light receiversinclude PIN photodiodes and MSM photodiodes. Optical couplers can alsobe used for optical receiver. From the above-described viewpoint,optical couplers to be applied to the optical receivers preferablyreceive light from all directions, or intra-planar 360°, and the use ofa conical or spherical mirror is therefore preferable.

A plurality of light receiving sections arranged in array may be usedfor a port. Particularly, the light receiving sections of the array maybe so arranged that light strikes the light receiving sections of thearray in different respective directions. Then, the direction from whichlight arrives can be discerned by selectively using the light receivingsections of the array. Alternatively, a light receiving section may beso arranged that it can selectively receive light being propagatedthrough the line waveguide.

The light transmission medium 101 may be arranged on an appropriatesubstrate. Substrates that can be used for arranging the lighttransmission medium 101 thereon include printed substrates, metalsubstrates such as aluminum substrates and SUS substrates, semiconductorsubstrates of Si substrates and GaAs substrates, insulating substratessuch as glass substrates and resin substrates or sheets of PMMA,polyimides and polycarbonates. FIG. 6 shows an embodiment ofoptoelectronic circuit according to the invention. In the optoelectronicwired substrate of FIG. 6, an electric wiring layer 106 carryingelectric wires 106 and electronic devices (LSI) 107 (107 a through 107 c) is laid on a film-like optical transmission medium 101 and electricsignals from the. electronic devices 107 are sent to any of the opticaltransmitters or optical receivers (ports 102). With this arrangement, asignal from an electronic device 107 is converted into an optical signalby an optical transmitter and then transmitted to an optical receiver byway of the line waveguide 108 or the two-dimensional orthree-dimensional waveguide 101 and then further to another electronicdevice 107.

As shown in FIG. 6, an electronic circuit comprising electronic devices107 and electric wires 106 connecting them and an optical circuit usingan optical transmission medium 101 coexist in an optoelectronic circuitaccording to the invention. A signal from an electronic device 107 isconverted into an optical signal in one of the ports 102 (102 a through102 c ) and the produced optical signal 103 is propagated through theoptical transmission medium 101 or the line waveguide 108 before it isconverted back into an electric signal by another one of the ports 102to establish an optical circuit.

The ports 102 have a function of transmitting or receiving an opticalsignal. More specifically, the ports comprise one or more than oneoptical transmitters adapted to convert an electric signal into anoptical signal or one or more than one optical receivers adapted toconvert an optical signal into an electric signal. However, from afunctional point of view, they preferably comprise both opticaltransmitters and optical receivers.

While FIG. 6 shows a cross sectional view of a relatively simple circuitthat comprises three ports 102, of which one is used for signaltransmission and another one is used for signal reception, it ispossible to arrange any given number of ports 102 at any desiredpositions on a plane as shown in a plan view of FIG. 8.

While the ports 102 are arranged on and held in contact with the opticaltransmission medium 101 in FIG. 6, they may alternatively be buried inthe optical transmission medium 101 so as to directly couple light tothe waveguide or arranged on any of the end facts of the opticaltransmission medium 101.

The electric wires 106 are metal wires made of aluminum, copper or thelike. They may be formed by vacuum evaporation or by using electricallyconductive paste and a screen printing technique. Alternatively, theymay be realized in the form of a circuit conductor pattern that isproduced by laying a metal foil such as an electrolytic copper foil andchemically etching the metal foil layer, using a piece of etching resistthat shows a desired pattern. Devices that can be used for theelectronic devices 107 may include electric parts such as resistors andcapacitors as well as ICs and LSI chips such as CPUs, RAMs and RFoscillators.

A circuit board according to the invention and having the abovedescribed configuration has characteristic features of an opticalcircuit such as high speed operation and immunity of EMIs and providesan enhanced degree of freedom in terms of designing it. Additionally,the connections of the optical circuit can be altered freely andappropriately because of the use of a two-dimensional orthree-dimensional optical waveguide.

Now, the present invention will be described further by way of examples.However, the present invention is by no means limited by the examplesbelow in terms of configuration and preparing process.

EXAMPLE 1

In Example 1, an optical transmission device having a configurationsimilar to that of FIGS. 1A through 1C is prepared. In this example, theoptical transmission medium 101 is made of fluorinated polyimide(refractive index: about 1.55) and has dimensions of 3 cm×5 cm. A singlelinear line waveguide 108 is buried so as to run horizontally in theoptical transmission medium 101 as shown in FIGS. 1A through 1C. Theline waveguide 108 shows a square cross section like that of 108(a) inFIG. 2 and each of the sides is about 25 microns long.

The refractive index of the line waveguide 108 is greater than that ofthe surrounding non-line section by about 1%. While both the linewaveguide and the non-line section are made of fluorinated polyimide,their refractive indexes can be differentiated by differentiating therespective fluorine contents. The illustrated structure is formed byforming a film layer of fluorinated polyimide that makes the non-linesection on a substrate, subsequently forming a line waveguide 108 andlaying a coating film that makes the non-line section. The linewaveguide 108 is formed by forming a film layer of fluorinated polyimidethat makes the line waveguide, subsequently forming a resist film,patterning the resist film by photolithography and dry-etching the filmlayer of fluorinated polyimide, using oxygen plasma.

The line waveguide 108 shows a cross section of about 25 microns andhence it is a line waveguide that propagates light in a relatively smallnumber of modes but not in a single mode. On the other hand, when lightis propagated through the optical transmission medium 101 that operatesas two-dimensional optical waveguide, the latter can propagate light ina large number of modes because it has a large thickness. FIG. 1C, whichis a cross sectional view taken along line 1C-1C in FIG. 1A illustrateshow a light beam 103B proceeds. It will be appreciated that a largenumber of beams of light can exist therein so as to be repeatedlyreflected by the top and bottom surfaces.

In this example, optical transmitters 121 (121A and 121B) and opticalreceivers 122 (122A and 122B) are mounted in the optical transmissionmedium 101 as shown in FIGS. 1A through 1C. The optical transmitter 121Aand the optical receiver 122A are separated from each other by adistance of about 4 cm, while the optical transmitter 121B and theoptical receiver 122B are separated from each other by a distance ofabout 1.5 cm. A surface emission type laser (wavelength of emitted laserbeam: 850 nm, output power; 3 mW) is used for each of the opticaltransmitters 121 and a PIN type photodiode of Si is used for each of theoptical receivers 122. 45° mirrors (not shown) are arranged as lightscattering bodies for the purpose of optically coupling the opticaltransmitters 121, the optical receivers 122, the line waveguide 108 andthe non-line section. A technique of forming a desired pattern on therear surface of the optical transmission medium 101 mechanically or bymeans of laser processing or etching and subsequently forming a metalfilm as mirror may be used to prepare the light scattering bodies.

The optical signal 103A output from the optical transmitter 121A andmodulated by 700 MHz is propagated through the line waveguide 108 andreceived by the optical receiver 122A. The optical signal 103B outputfrom the optical transmitter 121B and modulated by 400 MHz is coupled tothe non-line section. Since the reflection surface of the 45° mirrorthat corresponds to the optical transmitter 121B is made coarse, theoptical signal 103B is radiated with a radiation angle of about 60° andtransmitted through the optical transmission medium 101 before it isreceived by the optical receiver 122B. At this time, the optical signal103B partly passes through the line waveguide 108. In other words, theoptical transmission path of the line waveguide 108 and the opticaltransmission path that involves the use of the two-dimensional waveguideintersect each other. However, since the difference between therefractive index of the line waveguide 108 and that of the non-linesection is small and the dimensions of the cross section of the linewaveguide 108 is sufficiently small relative to the thickness of theoptical transmission medium 101, no problem of signal interference andoptical loss arises. Thus, both the optical signal 103A and the opticalsignal 103B can be transmitted simultaneously.

Referring to FIGS. 1A through 1C, while the optical signal 103B isreceived only by the optical receiver 122B, the optical signal 103B canalso be received at some other position if the optical signal 103B ispropagated to that position and another optical receiver is arrangedthere.

From the above description of the example, it will be appreciated thatthe line waveguide 108 and the two-dimensional waveguide are arranged soas to share the same space and used simultaneously to take differentroles. Thus, a compact optical transmission device that can be operatedwith an enhanced degree of inter-connect freedom is realized because theline waveguide and the two-dimensional waveguide operate in a single andsame layer with the above described arrangement.

EXAMPLE 2

In Example 2, an optical transmission device having a configurationsimilar to that of FIGS. 4A and 4B is prepared. FIGS. 4A and 4B showplan views of the same arrangement. In this example, the opticaltransmission medium 101 is made of PMMA (refractive index: about 1.49)and optical fibers of quartz of a single mode are buried in the opticaltransmission medium 101 for line waveguides 108. The optical fibers showa cross section similar to that of 108(f) in FIG. 2. Thus, the cores 132of the optical fibers operate as line waveguides 108 and the cladsections 131 of the optical fibers and the surrounding PMMA operate asnon-line section.

The cores and the clad sections of the optical fibers show respectivediameters of about 10 μm and about 125 μm and a relative refractiveindex of 0.2%. Since the optical transmission medium 101, or the PMMAlayer, has a thickness of 200 μm, it can be used as a multi-modetwo-dimensional optical waveguide, whereas the line waveguides 108 aresingle mode waveguides.

As shown in FIGS. 4A and 4B, the optical transmission medium 101 has asize of 3 cm square and is provided with optical ports 102 arranged onthe facets thereof, each of the optical ports 102 having an opticaltransmitter and an optical receiver. A total of four line waveguides 108are arranged horizontally in parallel with each other. Referring toFIGS. 4A and 4B, each of the optical ports 102 arranged at the lateralsides of the optical transmission medium 101 comprises an edge emissiontype laser (wavelength of emitted laser beam: 1,300 nm, output power; 5mW) as optical transmitter and its output is coupled to the related linewaveguide 108 by way of a lens and the corresponding facet of theoptical transmission medium 101.

Referring to FIGS. 4A and 4B, each of the optical ports 102 arranged atthe upper and lower sides of the optical transmission medium 101 alsocomprises an edge emission type laser (wavelength of emitted laser beam:1,300 nm, output power; 5 mW) as optical transmitter and its output isdirectly coupled to the optical transmission medium (non-line section)by way of the corresponding facet. Since the end facet of the opticaltransmission medium of the coupling section is made coarse, the outputoptical signal is diffused and propagated toward all the oppositelydisposed optical ports 102. The radiation angle is about 45°.

A PIN type photodiode of InGaAs is used for the optical receiver of eachof the ports 102. Referring to FIGS. 4A and 4B, the optical receivers ofthe optical ports 102 arranged at the lateral sides of the opticaltransmission medium 101 are mounted in such a way that they canselectively receive the optical signals from the line waveguides 108 byway of a lens. On the other hand, the optical receivers of the opticalports 102 arranged on the upper and lower sides of the opticaltransmission medium 101 are adapted to directly receive the opticalsignal from the optical transmission medium (non-line section).

In this example, the optical signal 103A is modulated by 800 MHz,whereas the optical signal 103B is modulated by 100 MHz. Referring toFIGS. 4A and 4B, part of the optical signal emitted from any of theports 102 arranged on the upper and lower sides of the opticaltransmission medium 101 crosses the line waveguides 108 but no problemof interferences occurs. This is because the line waveguides 108 have adiameter sufficiently smaller than the thickness of the opticaltransmission medium 101. Additionally, a wide margin is providedrelative to interferences because the optical device is so designed thatthe angle by which the optical signal 103B intersects the linewaveguides 108 is confined to a predetermined range (e.g., within arange between 45° and 90°).

Transversal communications from left to right and vice versa in FIGS. 4Aand 4B are based on fixed wiring using the line waveguides 108. Verticalcommunications from top to bottom and vice versa in FIGS. 4A and 4B canbe 1:N multicast communications. The current optical circuit can bealtered (reconfigured) by switching the signal transmitting port 102 asshown in FIGS. 4A and 4B.

As described above, the optical transmission device of this example canhandle high speed signals for optical transmissions between the portsarranged at the lateral sides of the device in FIGS. 4A and 4B by usingthe line waveguides. On the other hand, optical transmissions betweenthe ports arranged at the upper and lower sides of the device in FIGS.4A and 4B can be handled with an enhanced degree of inter-connectfreedom because the two-dimensional optical waveguide is used for them.In other words, the line waveguides and the two-dimensional waveguide inthis example are arranged and can be simultaneously used so as to sharea space and hence the circuit is provided both with flexibility and witha functional feature of high speed transmission. Particularly, a circuitboard where an electric circuit and an optical transmission deviceaccording to the invention and having a configuration as described abovecoexist will be adapted to freely alter the optical circuit.

EXAMPLE 3

In Example 3, an optical transmission device having a configurationsimilar to that of FIG. 5 is prepared. An optical transmission medium101 having a configuration similar to that of its counterpart of Example1 is also used in this example. In this example, the opticaltransmission medium 101 has a size of 3 cm square and is provided withoptical ports 102 adapted to transmit and receive data signals by way ofa plurality of line waveguides 108. A parallel transmission can beconducted between the ports that are linked together by way of aplurality of line waveguides 108. Apart from these ports, the opticaltransmission device additionally comprises a broadcast port 123 forbroadcasting a clock signal. The optical signal 103B from the broadcastport 123 is propagated through the optical transmission medium that is atwo-dimensional waveguide and received by the other ports 102.

Each of the ports 102 comprises an optical transmitter adapted to outputlight to the corresponding line waveguide 108, an optical receiveradapted to receive light from the corresponding line waveguide 108 andan optical receiver adapted to receive a clock signal propagated throughthe two-dimensional optical waveguide 101. The receivers for receivingthe clock of the transmission/reception ports 102 that are connected bythe line waveguides 108 are arranged at positions that are separatedfrom the broadcast port 123 by the same distance. In this example, dataare transmitted by way of the line waveguides 108 and a clock signal istransmitted from the broadcast port 123 to each of the ports 102. Theclock signals that are received by the transmission/reception ports 102do not show any difference of delay time because thetransmission/reception ports 102 are arranged at positions that areseparated from the broadcast port 123 by the same distance. Thus,bidirectional data transmission can be conducted efficiently by usingthe line waveguides 108 because clock signals are delivered withoutsignificant delays from the transmitters and the receivers.

EXAMPLE 4

In Example 4, an optoelectronic circuit board having a configurationsimilar to that of FIG. 6 is prepared. In other words, FIG. 6 is aschematic cross sectional view of the circuit board of this example,where an optical transmission medium 101 is sandwiched between a pair ofelectric wiring layers 105 a, 105 b and ports 102 (102 a through 102 c )are arranged near the interfaces of the electric wiring layer 105 a andthe optical transmission medium 101. The optical transmission medium 101is similar to its counterpart of Example 1. Both the substrate 100 andthe optical transmission medium 101 have a size of 3, cm square and atotal of 25 ports 102 are arranged in the form of matrix of 5×5 as shownin FIG. 8.

As shown in FIG. 8, only the ports 102 at the four corners are connectedby line waveguides 108. Only these ports 102 can utilize both opticalconnections using the line waveguides 108 and those using atwo-dimensional waveguide 101, whereas the remaining ports 102 canutilize only optical connections using the two-dimensional waveguide101.

Additionally, the optoelectronic circuit board of this example operatesas a densely mounted multilayer circuit board as a printed circuitboard, which electric circuit layer of electronic devices 107 (107 athrough 107 c ) and optical circuit layer is stacked in a manner asshown in FIG. 6. The signals from any of the electronic devices 107 thatare LSIs (such as CMOS logic signals) can be transmitted by light by wayof any of the ports 102 and the optical transmission medium 101 or theline waveguides 108. It is also possible to transmit a signal to one ormore than one nearby electronic devices 107 by way of electric wires106. The use of electric wires 106, the use of optical transmissionusing the line waveguides 108 or the use of free optical transmissionusing the two-dimensional waveguide 101 may be selected appropriatelydepending on the circumstances.

The logic signal from any of the LSIs 107 (3.3V in the case of CMOSs)provides voltage that is sufficiently high for driving the lightemitting element of a port 102. As the logic signal is applied to thelight emitting element of the port 102 as a forwardly biasing voltage,the electric signal being applied there is converted into an opticalsignal. Surface emission type lasers (VCSELs) of a 0.85 μm band are usedfor the light emitting elements. Each of the VCSELs is characterized bya drive current of 3.0 mA and an optical output level of 3 mW. Each ofthe ports 102 of this example comprises a VCSEL adapted to output asignal to any of the line waveguides 108 and a VCSEL adapted to outputan optical signal into the two-dimensional optical waveguide that is tobe diffused and propagated in all directions. Which mode of opticalpropagation is used depends on which VCSEL is driven.

The optical signal that is propagated through the optical transmissionmedium 101 is taken up by the light receiving element of a port 102 andconverted into an electric signal. An Si-PIN photodiode is used for thelight receiving element and connected to an electronic circuit 107. Theelectric signal produced by the conversion is taken into a nearby LSI asinput electric signal and processed there. At this time, if the lightreceiving element and a preamp for amplifying received signals areintegrally arranged, a CMOS compatible voltage can be restored. Thelight receiving section can be adapted to receive light from alldirections, or 360°, of any of the two-dimensional optical waveguides101 when a conical optical coupling section is used for it.

When the electronic devices and the optical devices of this example aredriven, it was confirmed that an optical circuit is established betweenany two ports 102 and operates in a desired manner. In other words, itwas confirmed that the optical circuit using both the line waveguides108 and the two-dimensional optical waveguide 101 operates effectivelyand so do the electric circuits 107.

An attempt for establishing free connections between two-dimensionallyarranged ports, using only line waveguides, requires communications byway of a plurality of ports or provision of a large number of opticalswitches for changing optical paths. To the contrary, this example,where a two-dimensional waveguide is used as an optical transmissionmedium, allows direct transmissions between ports that are separatedfrom each other by a long distance. The circuit board of this examplecomprises a two-dimensional optical waveguide that allows to freelychange connections in addition to electronic circuits and optical wiringusing line waveguides. Hence, it is a circuit board with an enhanceddegree of inter-connect freedom.

As described above, the present invention provides an opticaltransmission device that has a compact and simple configuration and isadapted to high speed data transmission and flexible inter-connect. Thepresent invention also provides an optoelectronic circuit that can behighly densely mounted with elements and provides an enhanced degree ofinter-connect freedom in addition to advantages of an optical circuitincluding high speed operation capabilities and immunity from EMIs.

1. An optical transmission device, comprising an optical transmissionmedium and a plurality of optical receivers, the optical transmissionmedium having a linear line waveguide, at least one of the opticalreceivers being adapted to receive a first optical signal propagatedthrough the line waveguide while at least one of the optical receiversbeing adapted to receive a second optical signal propagated through theoptical transmission medium.
 2. A device according to claim 1, furthercomprising a plurality of optical transmitters, and wherein the firstoptical signal is transmitted from at least one of the opticaltransmitters and is propagated through the line waveguide while thesecond optical signal is transmitted from at least one of the opticaltransmitter and is coupled to a non-line section of the opticaltransmission medium, which is the part thereof other than the linewaveguide, and propagated through the optical transmission medium.
 3. Adevice according to claim 2, wherein said line waveguide is made to showa complex refractive index greater than that of the non-line section ofthe optical transmission medium, which is the part thereof other thanthe line waveguide.
 4. A device according to claim 3, wherein thedifference between the complex refractive index of said line waveguideand that of said non-line section is not greater than 1%.
 5. A deviceaccording to claim 1, wherein said optical transmission medium is asheet-shaped two-dimensional optical waveguide.
 6. A device according toclaim 5, wherein the ½-th power of the cross sectional area of said linewaveguide is preferably not greater than ¼ of the thickness of theoptical transmission medium.
 7. An optoelectronic circuit, comprising anoptical transmission device as set forth in claim 5 and an electricwiring layer including electric wires and electronic devices, saidoptical transmission device and said electric wiring layer being laidone on the other, and said electric devices being connected to saidoptical transmitters or said optical receivers by way of the electricwires.
 8. A circuit according to claim 7, wherein the ½-th power of thecross-sectional area of said line waveguide is preferably not greaterthan ¼ of the thickness of the optical transmission medium.
 9. A deviceaccording to claim 2, wherein said optical transmission medium is asheet-shaped two-dimensional optical waveguide.
 10. A device accordingto claim 9, wherein the ½-th power of the cross sectional area of saidline waveguide is preferably not greater than ¼ of the thickness of theoptical transmission medium.
 11. An optoelectronic circuit, comprisingan optical transmission device as set forth in claim 9 and an electricwiring layer including electric wires and electronic devices, saidoptical transmission device and said electric wiring layer being laidone on the other, and said electric devices being connected to saidoptical transmitters or said optical receivers by way of the electricwires.
 12. A circuit according to claim 11, wherein the ½-th power ofthe cross-sectional area of said line waveguide is preferably notgreater than ¼ of the thickness of the optical transmission medium. 13.A device according to claim 3, wherein said optical transmission mediumis a sheet-shaped two-dimensional optical waveguide.
 14. A deviceaccording to claim 13, wherein the ½-th power of the cross sectionalarea of said line waveguide is preferably not greater than ¼ of thethickness of the optical transmission medium.
 15. An optoelectroniccircuit, comprising an optical transmission device as set forth in claim13 and an electric wiring layer including electric wires and electronicdevices, said optical transmission device and said electric wiring layerbeing laid one on the other, and said electric devices being connectedto said optical transmitters or said optical receivers by way of theelectric wires.
 16. A circuit according to claim 15, wherein the ½-thpower of the cross-sectional area of said line waveguide is preferablynot greater than ¼ of the thickness of the optical transmission medium.17. A device according to claim 4, wherein said optical transmissionmedium is a sheet-shaped two-dimensional optical waveguide.
 18. A deviceaccording to claim 17, wherein the ½-th power of the cross sectionalarea of said line waveguide is preferably not greater than ¼ of thethickness of the optical transmission medium.
 19. An optoelectroniccircuit, comprising an optical transmission device as set forth in claim17 and an electric wiring layer including electric wires and electronicdevices, said optical transmission device and said electric wiring layerbeing laid one on the other, and said electric devices being connectedto said optical transmitters or said optical receivers by way of theelectric wires.
 20. A circuit according to claim 19, wherein the ½-thpower of the cross-sectional area of said line waveguide is preferablynot greater than ¼ of the thickness of the optical transmission medium.